1. Field of the Invention
The present invention relates to a fuel injection pump. For instance, the present invention can be suitably applied to a fuel injection pump used in an accumulation type fuel injection system of a diesel engine.
2. Description of Related Art
There is a fuel injection pump having a main shaft, a cam ring and at least one plunger, for instance, as disclosed in Unexamined Japanese Patent Application Publication No. 2003-148295 (Patent Document 1, hereafter) or No. 2002-250459 (Patent Document 2, hereafter). As shown in FIG. 5, a cam 144 having a circular section is integrally formed on the main shaft 110. The cam ring is rotatably fitted to an outer periphery of the cam 144 through a bush. The plunger is held inside a cylinder so that the plunger can reciprocate in the cylinder. If an engine drives the maim shaft 110 to rotate, the rotational movement of the cam 144 is transmitted to the plunger through the cam ring. Thus, the plunger reciprocates inside the cylinder and pressure-feeds the fuel. The fuel injection pump has two fuel pressurizing chambers, which are alternately pressurized by the two reciprocating plungers. The fuel injection pump has discharge valves for alternately discharging the fuel pressurized in the fuel pressurizing chambers.
In the technology disclosed in Patent Document 1, a restriction portion is formed in a bypass passage leading from a feed pump to a cam chamber for restricting a quantity of lubrication fuel supplied into the cam chamber. Thus, a feeding pressure required to fill the fuel pressurizing chamber with the fuel is ensured even when rotation speed is low. The restriction portion is formed so that a flow passage of the restriction portion is not blocked completely even if extraneous matters included in the fuel reach the restriction portion.
The fuel injection pump disclosed in Patent Document 2 includes a suction quantity control electromagnetic valve for supplying the fuel into the fuel pressurizing chamber and for controlling the quantity of the fuel pressurized and pressure-fed by the plunger. A valve member and an armature of the suction quantity control electromagnetic valve are formed with penetration passages axially penetrating the valve member and the armature. The suction quantity control electromagnetic valve is formed with a communication passage for connecting an upstream passage of control fuel with an armature chamber. Since a flow of the fuel is generated in the armature chamber, the fuel will not stay around the armature. Therefore, even if the extraneous matters included in the fuel exist in the armature chamber, the extraneous matters will be discharged outward along the flow of the fuel.
The above technologies can prevent blocking of the fuel lubrication bypass passage leading to the cam chamber or defective operation of the suction quantity control electromagnetic valve due to the extraneous matters included in the fuel. However, there is a possibility that the extraneous matters get stuck among operating members such as the cam, the cam ring, the plunger, the suction valve and the discharge valve, which are disposed downstream of the fuel lubrication bypass passage and housed in the cam chamber or are disposed downstream of the suction quantity control electromagnetic valve for performing rotation movement, reciprocating movement and the like. If water and the like are accidentally mixed into the fuel, there is a possibility that poor lubrication (deterioration of lubricity) occurs among the sliding members such as the plunger housed in the cam chamber. The poor lubrication between the plunger and an inner peripheral surface of a plunger sliding hole can cause seizing of the plunger. The seizing of the plunger triggers seizing of sliding surfaces of the plunger and the cam ring, which revolves. As a result, there is a possibility that an excessive thrust force is applied to the cam ring and the plunger is damaged.
If the extraneous matters get stuck at a seat portion of the operating member such as the suction valve or the discharge valve, fluid-tightness of a sealing portion cannot be ensured and an appropriate pressure-feeding quantity (a discharging quantity) of the fuel cannot be obtained. In addition, high pressure of the continuously pressurized fuel is applied to the plunger. If the high pressure of the fuel is continuously applied to the plunger, the poor lubrication can occur between the plunger and the inner peripheral surface of the plunger sliding hole and the seizing of the plunger can be caused. In this case, there is a possibility that the excessive thrust force is applied to the cam ring and the plunger is damaged.
If the plunger is damaged, there is a possibility that fragments of the damaged plunger move through the cam chamber and get stuck into a clearance between the housing and the cam ring. In this case, if the housing is made of aluminum, there is a possibility that the housing is damaged and the damage spreads.
In order to prevent the above trouble, the clearance between the housing and the cam ring can be enlarged. However, in this case, body size is increased to a large extent. Therefore, cost will be increased and mountability to a vehicle and the like will be deteriorated.
In the case where the fuel is stored in a metal drum and the like and is supplied from the metal drum to the vehicle, the water can be accidentally mixed into the fuel. The water easily accumulates in the bottom of the metal drum. Therefore, there is a possibility that the fuel including a large amount of water is used in the fuel injection pump if the fuel is supplied from the metal drum.